The present invention relates generally to an arrangement for supporting roofs of underground excavations and other mining galleries. More particularly, the invention relates to improvements in so-called walking mine roof supports which are movable stepwise towards the mine face in an underground excavation.
Mine roof supporting arrangements generally comprise a mobile floor-engaging support which supports a roof shield. A rear shield is pivotally connected to the roof shield and reinforces the supporting function of the roof shield, as well as preventing any loose ore from the roof from falling into the interior of the mine roof supporting arrangement, thereby interfering with the stepwise advancement thereof. It has been proposed to use separate pit props to individually move each shield toward and away from the support.
However, the known prior-art arrangements are particularly disadvantageous in low height underground excavations because the rear shield is forced to lie along a plane which defines a very small angle relative to the plane of the floor of the excavation. Put another way: the rear shield cannot effectively reinforce the roof shield, nor divert loose ore in direction away from the mine face because of its slight slope relative to the plane of the floor.
Moreover, the possibility exists that the mine roof will generate a reaction force at the pivot connection between the rear and roof shields which will cause the rear end of the rear shield to be raised above the front end of the rear shield. The rear and roof shields thereby assume a V-shaped configuration having its open end facing the roof.
This condition is extremely dangerous. The rear end of the rear shield now engages the roof and restricts free advancement towards the mine face. The pit props cannot be further retracted to permit disengagement of the rear shield because the pit props are already in their fully retracted position in such extremely low excavations. In the event that the mine roof supporting arrangement is advanced in this relative orientation between the shields, the danger of cave-in is greatly increased. Miners are now subject to injury and death; and mine equipment are now subject to damage and destruction.
Furthermore, such low excavations cause extremely large reaction forces to be generated at all of the hinged connections between the pit props and the roof shield, the rear shield and the support. These forces tend to destroy all of these hinged connections, thereby making the entire mine roof supporting arrangement unusable.